Automatic polishing device for surface finishing of complex-curved-profile parts

ABSTRACT

The present invention discloses an automatic polishing device and the method of using the device for the surface finishing of a workpiece such as complex-curved-profile parts. Automatic polishing is performed by mounting the workpiece on an apparatus which enables different orientations along multiple axes and immerging the workpiece in a controlled flow of abrasive slurry. The device of the present invention provides a uniform finish on free form surface. It is also precise, low cost, non-destructive, and non-polluting.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from the U.S. provisionalapplication Ser. No. 61/686,852 filed on Apr. 13, 2012, the disclosureof which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to an automatic polishing device, in particular,to a flow-based polishing device for the surface finishing ofcomplex-curved-profile parts.

TECHNICAL BACKGROUND

Polishing is an essential process of creating a smooth and shiny surfaceby using mechanical or chemical reaction and it has been employed bymanufacturing industry for centuries. Comparing with hand-polishing, theprocess using automated polishing machines, such as those used forpolishing semiconductor wafers and for polishing fine optics, are moreefficient. However, the use of these automated polishing machines isrestricted to those parts with surface profiles in regular shape.Therefore, hand-polishing is still widely used in a number of industries(e.g., watch, jewelry, mould and die, etc.) as in many circumstances,the surface profiles of the polishing parts are not in regular shape asthose of semiconductor wafers or optical lenses. Most of the existingautomated polishing machines just could not be applied to thecomplex-curved-profile parts, such as small watch parts and jewelryparts that are made of metal or metal alloy, jade stone, ivory, andceramics, etc. There are considerable needs to develop an efficientautomated polishing technique yet with the flexibility as skilled hands.Moreover, the machine-based polishing technique would yield a moreuniform and reliable polishing effect comparing to those done byhand-polishing. It is believed that hand-polishing can reach the bestsurface roughness of R>0.1 μm, while machine-based polishing can reducethe surface roughness by one order of magnitude. This is essential, forexample, for the mould-and-die industry which requires a precise surfacetreatment of molding-tool-steel.

Many prior arts have attempted to overcome the difficulties of surfacefinishing of complex-curved-profile parts. U.S. Pat. No. 6,171,175 hasdisclosed a hand polishing method using conventional grinding, lapping,honing techniques, or an automatic polishing method with improvedadaptive mechanical tools but none of these methods can give enoughprecision at acceptable efficiency. Computer programmed roboticpolishing (European Pat. No. EP1935564), magnetorheological polishing(U.S. Pat. No. 5,449,313), or ion beam machining (US Patent ApplicationPub. No. 20070227878) possess high precision but the capital cost is toohigh. The flow-based machining, e.g., abrasive flow machining (U.S. Pat.No. 4,936,057), magnetic abrasive finishing (U.S. Pat. No. 4,175,930),fluid jet polishing (U.S. Pat. No. 7,455,573), can balance therequirements of precision and cost but only working for hard workpieceswith strength against the flow force. The chemical polishing (U.S. Pat.No. 4,826,563), electrochemical polishing (U.S. Pat. No. 4,740,280), andplasma-electrolytic polishing (US Patent Application Pub. No.20100200424) provide a solution of precise, gentle and low-cost surfacefinishing. However, the treatment and disposal of used chemicals andwaste water are troublesome. Such wet-polishing processes involvingchemical reactions are restricted due to environmental regulations inmany circumstances. The disclosure of these cited references and theirentirety are incorporated herein by reference.

There is a need for a new polishing means which is low-cost,environmental-friendly, precise, gentle and suitable for various typesof workpiece including complex-curved-profile parts.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide an alternate polishingdevice. The device includes a bath of controlled flow of abrasiveslurry, at least one apparatus for mounting at least one workpiece withwhich its orientation varies along multi-axes, and at least onecontainer containing the abrasive slurry. The device of the presentinvention provides a uniform finish on a free form surface. It is alsoprecise, low cost, non-destructive, and non-polluting. The at least oneapparatus for mounting the at least one workpiece includes a firstrotary stage which can be a one-axis, two-axis, or three-axis rotarystage and is immerged inside flow of abrasive slurry during operation ofthe device. The first rotary stage is automatically adjustable such thatthe orientation of the mounted workpiece varies in a controlled manner.The abrasive slurry comprises a plurality of abrasive particles and acarrying liquid which is driven by a liquid pump. Optionally, theabrasive slurry includes a plurality of abrasive particles which ispre-mixed with a plurality of elastic polymer particles and the carryingliquid. Alternatively, a plurality of relatively smaller abrasiveparticles can be pre-coated on the surface of a relatively largerelastic polymer particle. The relatively larger elastic polymer particlemay further include a magnetic core to facilitate the flow of theabrasive slurry driven by a plurality of magnetic bars situated underthe container. Depending on the shape of the workpiece, the device ofthe present invention may be further modified to include a second rotarystage for driving the rotation of the first rotary stage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of the device having acircular container for holding an abrasive slurry and a three-axisrotary stage for mounting a workpiece to be polished. Abrasive flow isdriven by a liquid pump.

FIG. 2 is a schematic diagram of another embodiment of the device havinga circular container for holding an abrasive slurry and a three-axisrotary stage for mounting a workpiece to be polished. The abrasiveslurry contains magnetic particles and abrasive flow is driven byelectromagnetic force. The inset shows the structure of the magneticabrasive slurry.

FIG. 3 is a schematic diagram of a further embodiment of the devicehaving a cylindrical container for holding an abrasive slurry and atwo-axis rotary stage for mounting a workpiece to be polished. Therelative movement between the abrasive slurry and the workpiece isachieved by rotating the cylindrical container.

FIG. 4 is a schematic diagram of other embodiment of the device having afixed (non-rotatable) cylindrical container for holding an abrasiveslurry and a first one-axis rotary stage for mounting a workpiece. Therelative movement between the abrasive slurry and the workpiece isachieved by rotating the first rotary stage inside the cylindricalcontainer with a second rotary stage outside of the cylindricalcontainer.

FIG. 5 shows the surface roughness of a steel work piece before andafter polishing using the method in one of the embodiments illustratedin FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary embodiment of the present invention. Theautomatic polishing device in this embodiment comprises a circularcontainer 11 containing an abrasive slurry 12 which comprises aplurality of abrasive particles and a carrying liquid driven by a liquidpump 13, wherein the liquid pump 13 drives the abrasive slurry to formabrasive slurry flow 12 in the circular container 11. A workpiece 15 tobe polished is mounted in a three-axis rotary stage 16 immerged insidethe abrasive slurry flow 12. The orientation of the workpiece 15 variesin a controlled manner by the three-axis rotary stage 16 capable ofautomatic adjustment to facilitate a gentle and uniform surface finishof the workpiece 15. In one example, the workpiece 15 is acomplex-curved-profile aluminum article at dimension of less than50(L)×50(W)×50(H)mm³. It is immerged in the abrasive slurry 12containing 600 mesh silicon carbide (SiC) abrasive particles, otherpolymers such as silicone-based elastic polymer, and a carrying liquid.The abrasive slurry flow 12 is driven by the liquid pump 13 inside thecircular container 11. The circular container 11 is made of plastic andthe inner diameter of the container 11 is 200 mm and the outer diameteris 400 mm and the height is 400 mm. Comparing with containers of othershapes (e.g., the cylindrical container), the circular container 11confines the flow of the abrasive slurry 12 in a circular track atrelatively constant speed ranging from 0.3-3.0 m/s. The relativemovement between the abrasive slurry 12 and the workpiece 15 yields anadaptive polishing of a curved surface. In the meantime, with theautomatic three-axis rotary stage 16, the orientation of the workpiece15 slowly varies along three axes periodically at the rate of ˜one cycleper minute, so that a uniform surface polishing can be achieved. In suchoperation, the as-cut workpiece 15 can reach a mirror-like shinningsurface in 30-60 min.

FIG. 2 illustrates another embodiment of the present invention having acircular container 21 for holding a magnetic abrasive slurry 22 and athree-axis rotary stage 23 for mounting a workpiece 24 to be polished.The magnetic abrasive slurry 22 in this embodiment comprises a pluralityof elastic polymer particles of about 1 mm in size. Each of the elasticpolymer particles has a magnetic core inside the particle and aplurality of abrasive particles of about 1-100 μm in size which arepre-coated on the surface of the elastic polymer particle. The magneticabrasive slurry 22 in this embodiment flowing inside the circularcontainer 21 is driven by a plurality of magnets on a magnetic board 25driven by a motor 26 for rotating under the circular container 21. Theworkpiece 24 to be polished is mounted in the three-axis rotary stage 23immerged inside the magnetic abrasive slurry flow 22. The orientation ofthe workpiece 24 varies in a controlled manner by the three-axis rotarystage 23 capable of automatic adjustment to facilitate a gentle anduniform surface finish of the workpiece 24. In one example, theworkpiece 24 is a complex-curved-profile steel article at the dimensionof less than 50(L)×50(W)×50(H)mm³. It is immerged in the magneticabrasive slurry 22 comprising silicone-based elastic polymer particlesof about 1 mm in size. Each of the elastic polymer particles has amagnetic core of specially-treated magnetic stainless steel of 0.3mm(D)×1 mm(L) pin inside the particle. A plurality of SiC abrasiveparticles of about 1-100 μm in size which are pre-coated or glue-mixedon the surface of the elastic polymer particle. The magnetic abrasiveslurry 22 in such is flowing inside the circular container 21, driven bya plurality of magnets rotating under the circular container 21 or aplurality of electromagnets under the circular container 21 alternatingthe electromagnetic field inside the circular container 21. The circularcontainer 21 is made of plastic and the inner diameter of the container21 is 200 mm and the outer diameter is 400 mm and the height is 400 mm.The circular container 21 confines the flow of the magnetic abrasiveslurry 22 in a circular track and the magnetic abrasive slurry 22 flowdriven by the magnetic force runs as fast as 30 Hz. Moreover, itautomatically switches direction between clockwise and counter-clockwiseonce a minute with pre-setting. The relative movement between suchmagnetic abrasive flow and the workpiece 24 yields an efficientpolishing of curved surface. In the meantime, with the automaticthree-axis rotary stage 23, the orientation of the workpiece 24 slowlyvaries along three axes periodically at the rate of ˜one cycle perminute, so that a uniform surface polishing can be achieved. In suchoperation, the use of carrying liquid in abrasive slurry is optional.That is, the polishing process can be achieved with a ‘dry flow’ of themagnetic-abrasive-polymer particles. In certain embodiments, this isconvenient that the workpiece 24 needs not to be in contacted with wateror oil. Depending on the size and surface complexity, the as-cutworkpiece 24 can reach a mirror-like shinning surface in 30-60 min withthis method. FIG. 5 shows the surface profile of a steel workpiecesample treated as such measured with Alpha Step from Tencor Instruments.As a direct readout from the Instrument, the surface roughness (Ra)improves from 3.7 μm to 0.1 μm after the said polishing treatment.

FIG. 3 illustrates a further embodiment of the present invention. Anabrasive slurry 31 in this embodiment comprises a plurality of abrasiveparticles which are pre-mixed with a plurality of elastic polymerparticles and a carrying liquid. The abrasive slurry 31 is held in acylindrical container 32 which is about 400 mm in diameter androtatable, as such, the abrasive slurry 31 rotates together with therotating cylindrical container 32 driven by a rotating stage 33connected to the bottom of the cylindrical container 32. The rotatingstage 33 is further driven by a motor 34. The workpiece 35 to bepolished is mounted in a two-axis rotary stage 36 immerged inside theabrasive slurry flow and about 100-150 mm away from the rotating axis atthe centre of the cylindrical container 32. The orientation of theworkpiece 35 varies in a controlled manner by the two-axis rotary stage36 capable of automatic adjustment to facilitate a gentle and uniformsurface finish of the workpiece 35. In one example, the workpiece 35 isa mammoth task figure at the dimension of less than50(L)×50(W)×50(H)mm³.The abrasive slurry 31 contains 1200 mesh Al₂O₃abrasive particles and silicone-based elastic polymer particles and anoil-based carrying liquid. The abrasive slurry 31 is held in thestainless steel cylindrical container 32 at the diameter of 400 mm andthe height of 400 mm. The abrasive slurry 31 rotates together with therotating cylindrical container 32 driven by a rotating stage 33connected to the bottom of the cylindrical container 32 at the rate of60-600 rpm. The workpiece 35 is mounted in the two-axis rotary stage 36immerged inside the abrasive slurry flow at about 100-150 mm away fromthe rotating axis at the centre of the cylindrical container 32. Sucharrangement results in a relative movement between the abrasive slurry31 and the workpiece 35 at the linear speed of 1-10 m/s. With therelatively fine and soft abrasive slurry 31 used, the rotation providesa gentle polishing on a complex-curved surface of relatively softmaterial. For the workpiece 35 such as a mammoth task figure, only theoutline along the vertical axis of the figure needs to be polished. Thebottom surface to support the figure is flat and treated with othermeans. In this special case, the multi-axis rotary stage that mounts theworkpiece 35 can be simplified as the two-axis rotary stage 36, and thefigure to be polished is mounted with vertical axis along with one ofthe rotary axis as shown in the FIG. 3. With the automatic two-axisrotary stage 36, the orientation of the workpiece 35 slowly varies alongtwo axes periodically at the rate of ˜one cycle per minute, so that auniform surface polishing can be achieved. Depending on the finest orcolor effect required, the polishing process of such a delicateworkpiece 35 takes about 1-10 hours.

FIG. 4 illustrates other embodiment of the present invention. Anabrasive slurry 41 in this embodiment comprises a plurality of abrasiveparticles of about 1-100 μm in size which are pre-coated on the surfaceof each of the elastic polymer particles of about 100-1000 μm in size.The abrasive slurry 41 is held in a fixed (non-rotatable) cylindricalcontainer 42 of about 400 mm in diameter. A workpiece 43 (e.g., apatterned stainless steel sheet) to be polished is mounted in a one-axisrotary stage 44 immerged inside the abrasive slurry 41 flow and about100-150 mm away from the central axis of the fixed cylindrical container42. The first rotary stage 44 is further mounted on a second rotarystage 45 rotating along the central axis of the fixed cylindricalcontainer 42. The second rotary stage 45 is driven by a motor 46. Whilethe orientation of the workpiece 43 varies in a controlled manner by thefirst rotary stage 44 capable of automatic adjustment, the relativemovement between the abrasive slurry 41 and the workpiece 43 is drivenby the second rotary stage 45, and as such a gentle and uniform surfacefinish of the workpiece is achieved. In one example, the abrasive slurry41 comprised silicone-based elastic polymer particles of about 100-1000μm in size. A plurality of SiC abrasive particles of about 1-100 μm insize are pre-coated or glue-mixed on the surface of the elastic polymerparticle. The abrasive slurry 41 is held in the fixed (non-rotatable)stainless steel cylindrical container 42 at the diameter of 400 mm andthe height of 400 mm. The workpiece 43 is a patterned stainless steelsheet of the size of 100(L)×50(W)×0.5(H)mm³. The typical dimensions ofthe through-patterns (holes and lines) on the sheet are ranging from0.5-5 mm, and it requires smooth lines and edges at-finish on both sidesof the sheet. In order to polish the through-patterns of the stainlesssteel sheet, the abrasive slurry 41 must flow across the sheet, passingthrough the patterns at appropriate force that does not deform the 0.5mm-thick sheet. In this specific embodiment, the rotary stage thatmounts the sample can be simplified as the one-axis rotary stage 44. Inthe setup, the workpiece 43 is mounted in the first one-axis rotarystage 44 so that the center line along longitude direction of the sheetis aligned with the rotary axis of the one-axis rotary stage 44. Itrotates slowly along this axis at the rate of ˜one cycle per minute toprovide a uniform operation. On the other hand, the first rotary stage44 is further mounted on the second rotary stage 45, which is driven bythe motor 46 and suspends on top of the container 42. The second rotarystage 45 rotates along the central axis of the cylindrical containersuch that the workpiece 43 is immerged inside the abrasive slurry 41 atabout 100-150 mm away from the central axis. While the second rotarystage 45 rotates at the rate of 60-600 rpm, the workpiece 43 furtherrotates in the abrasive slurry 41 along the central axis at the linearspeed of 1-10 m/s, in addition to the foresaid slow rotation driven bythe first rotary stage 44. While the relative movement between theabrasive slurry 41 and the workpiece 43 is governed by the fast rotationdriven by the second rotary stage 45, the orientation of the workpiece43 is controlled by the slow rotation driven by the first rotary stage44. Even though stainless steel is a hard material, the deburing processof the pattern edges can be achieved in this operation within one hourduration.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with each other. Furthermore, ifdesired, one or more of the above-described functions/embodiments may beoptional or may be combined.

For example, the abrasive slurry might be composed of:

-   -   (a) abrasive particles and carrying liquid; or    -   (b) abrasive particles and elastic polymer particles; or    -   (c) abrasive particles and elastic polymer particles and        carrying liquid; or    -   (d) abrasive particles and magnetic particles; or    -   (e) abrasive particles and magnetic particles and carrying        liquid; or    -   (f) abrasive particles and magnetic particles and elastic        polymer particles; or    -   (g) abrasive particle and magnetic particles and elastic polymer        particles and carrying liquid; and the abrasive particles are        not limited to SiC or Al₂O₃ particles as mentioned in the above        descriptions.

In terms of industrial applications, the container and the rotary stagecan be readily scaled up to meet the needs in various applications.Multiple containers engaged with single or multiple driving forces andmultiple rotary stages for mounting multiple workpieces in eachcontainer can be applied.

Although various aspects of the invention are set out in the independentclaims, other aspects of the invention comprise other combinations offeatures from the described embodiments and/or the dependent claims withthe features of the independent claims, and not solely the combinationsexplicitly set out in the claims.

It is also noted herein that while the above describes exemplaryembodiments of the invention, these descriptions should not be viewed ina limiting sense. Rather, there are several variations and modificationswhich may be made without departing from the scope of the presentinvention as defined in the appended claims.

INDUSTRIAL APPLICABILITY

The present invention is useful for polishing both regular and irregularshaped objects in a fully automated polishing process to replace theconventional manual polishing or partially automated polishing process.The setup of the automatic polishing device is flexible and thecomposition of the abrasive slurry flow could also be modified to suitdifferent shapes and size of the workpiece. The multi-axis rotary stageof the mounting apparatus in the present invention also enablesdifferent orientations of the movement of the workpiece along differentaxes during the automatic adjustment.

What we claim:
 1. An automatic polishing device for the surfacefinishing of a workpiece comprising at least one container for holdingan abrasive slurry; one or more driving apparatuses for controlling therelative movement between said abrasive slurry and the workpiece in saidabrasive slurry; and one or more mounting apparatuses for mounting atleast one workpiece inside said abrasive slurry, wherein said one ormore mounting apparatuses automatically adjust the orientation of saidat least one workpiece along one or more axes in a controlled manner. 2.The device of claim 1, wherein said abrasive slurry comprises one ormore of a plurality of abrasive particles, a carrying liquid, aplurality of elastic polymer particles, and/or a plurality of magneticparticles.
 3. The device of claim 1, wherein said abrasive slurry ismagnetic or non-magnetic.
 4. The device of claim 2, wherein saidabrasive particles are silicon carbide (SiC) and/or aluminum oxide(Al₂O₃).
 5. The device of claim 1, wherein said one or more drivingapparatuses provides a controlled driving force for controlling therelative movement between said abrasive slurry and said at least oneworkpiece in said abrasive slurry by exerting mechanical force,electromagnetic force, or a combination of both mechanical andelectromagnetic forces.
 6. The device of claim 1, wherein said one ormore driving apparatuses comprises one or more of liquid pumps, magneticboards, rotating stages and/or rotary stages.
 7. The device of claim 1,wherein said relative movement is carried out by immerging said at leastone workpiece in a flow of said abrasive slurry or by moving said atleast one workpiece in a static abrasive slurry.
 8. The device of claim1, wherein said orientation of said at least one workpiece varies alongone axis, two axes, or three axes.
 9. The device of claim 1, whereinsaid at least one container is circular; said one or more drivingapparatuses is a liquid pump; said one or more mounting apparatusescomprises a three-axis rotary stage to enable the orientation of said atleast one workpiece along three different axes in a controlled manner;said abrasive slurry comprises a plurality of abrasive particles and acarrying liquid driven by said liquid pump to create a flow of saidabrasive slurry.
 10. The device of claim 1, wherein said at least onecontainer is circular; said driving apparatus is a magnetic boardsituated below said container; said one or more mounting apparatusescomprises a three-axis rotary stage to enable the orientation of said atleast one workpiece along three different axes in a controlled manner;said abrasive slurry comprises a plurality of abrasive particles, aplurality of elastic polymer particles and a plurality of magneticparticles, and wherein said abrasive particles of about 1-100 μm arepre-coated on each of said elastic polymer particles of about 1 mm whilesaid magnetic particles are embedded into the core of each of saidelastic polymer particles.
 11. The device of claim 1, wherein said atleast one container is cylindrical and rotatable with a diameter ofabout 400 mm; said one or more driving apparatuses is a rotating stageconnected to the bottom of said container; said one or more mountingapparatuses comprises a two-axis rotary stage to enable the orientationof said at least one workpiece along two different axes in a controlledmanner and is situated about 100-150 mm away from the rotating axis atthe centre of said at least one container; said abrasive slurrycomprises a plurality of abrasive particles, a plurality of elasticpolymer particles and a carrying liquid, and wherein said abrasiveparticles are pre-mixed with said elastic polymer particles.
 12. Thedevice of claim 1, wherein said at least one container is cylindricaland non-rotatable; said one or more driving apparatuses comprises asecond rotary stage; said one or more mounting apparatuses comprises afirst rotary stage capable of moving said at least one workpiece mountedon said mounting apparatuses along one axis in a controlled manner whichis situated about 100-150 mm away from the central axis of saidcontainer, and the distal end of said first rotary stage is furtherconnected to said second rotary stage; said abrasive slurry comprises aplurality of abrasive particles of about 1-100 μm, a plurality ofelastic polymer particles of about 100-1000 μm, and a carrying liquid,and wherein said plurality of abrasive particles are pre-coated on thesurface of each of said elastic polymer particles.
 13. A workpiecepolished by the device of claim 1 comprises complex-curved-profileparts, irregular shaped article, and/or regular shaped article, whereinsaid workpiece is made of metal or non-metal material.